1. Field of the Invention
The present invention relates to a semiconductor device having a circuit formed using a thin film transistor (hereinafter referred to as a TFT) and a manufacturing method thereof. For example, the present invention relates to an electronic appliance in which an electro-optical device typified by a liquid crystal display panel or a light-emitting display device including an organic light-emitting element is mounted as its component.
Note that the semiconductor device in this specification refers to all the devices which can operate by using semiconductor characteristics. An electro-optical device, a semiconductor circuit, and an electronic appliance are all semiconductor devices.
2. Description of the Related Art
Various metal oxides are used for a variety of applications. Indium oxide is a well-known material and is used as a transparent electrode material which is necessary for liquid crystal displays and the like.
Some metal oxides have semiconductor characteristics. As metal oxides having semiconductor characteristics, for example, tungsten oxide, tin oxide, indium oxide, zinc oxide can be given. References disclose a thin film transistor in which such a metal oxide having semiconductor characteristics is used for a channel formation region (Patent Documents 1 to 4 and Non-Patent Document 1).
Further, not only single-component oxides but also multi-component oxides are known as metal oxides. For example, InGaO3(ZnO)m (m is a natural number), which is a homologous compound, is known as a multi-component oxide semiconductor including In, Ga, and Zn (Non-Patent Documents 2 to 4).
Furthermore, it is confirmed that an oxide semiconductor including such an In—Ga—Zn-based oxide is applicable to a channel layer of a thin film transistor (Patent Document 5 and Non-Patent Documents 5 and 6).